Photovoltaic devices, such as photocells, are an important energy source that has thus far remained underutilized for widespread energy production due to undesirable efficiency and/or production cost factors. For example, conventional photocells comprise a silicon-based substrate that includes a large-area p-n junction. Crystalline semiconductor substrates, such as silicon, are expensive, making production of photocells cost prohibitive for many applications. Further, photocells generate electrical energy by converting photons from a light source into electricity (e.g., by freeing electron-hole pairs). Conventional photocells typically provide a light-to-electricity conversion efficiency of only up to about 25%. This low conversion efficiency similarly makes photocells an undesirable option for many applications.
Attempts have been made to increase photocell energy conversion efficiency. Some of the attempts have employed nanotechnology as a tool. See, for example, U.S. Patent Application No. 2005/0009224 filed by Yang et al., entitled “Nanowire Array and Nanowire Solar Cells and Methods for Forming the Same” (wherein nanowire oxides are used in conjunction with a charge transport medium in optoelectronic devices); U.S. Patent Application No. 2005/0214967 filed by Scher et al., entitled “Nanostructure and Nanocomposite Based Compositions and Photovoltaic Devices” (wherein nanostructures, such as core-shell nanocrystals, are used in photovoltaic devices oriented horizontally along the plane of the electrodes); and Kayes et al., Comparison of the Device Physics Principles of Planar and Radial p-n Junction Nanorod Solar Cells, 97 J. APPL. PHYS. 114302 (2005) (wherein radial p-n junction nanorod solar cells are described).
As these references show, nanotechnology can be employed in photovoltaics. However, improved techniques for combining these technologies to cost-effectively produce more efficient photovoltaic devices are needed.